Premenopausal women at increased risk for breast cancer based on a family history of disease will be eligible for this randomized trial to one of three arms: LY353881yHCl, tamoxifen or placebo for 6 months. The objectives of the study are 1) to determine the safety of the class of SERMs in premenopausal women by monitoring the effects on bone mineral density, the ovary, ovarian function, and lipids; 2) biomarkers of breast cancer will be developed by sampling the breasts of the high risk women and determining the biomarkers that are modulated by the agents compared with placebo; 3)serum biomarkers will be evaluated with IGF1 and IGFB3 levels pre and post treatment and ; 4) the feasibility of accrual of premenopausal women with a potential for a genetic predisposition to a chemoprevention study will be evaluated.